Field of the Invention
The present invention relates to a method of drying honeycomb formed bodies. More specifically, the present invention relates to a method of drying honeycomb formed bodies with which they cannot easily be affected by an atmosphere in a dry space and can be dried without occurrence of deformation and cracks of outer peripheries thereof even when partition walls thereof are thin.
Description of Related Art
A honeycomb structure made of ceramics has been widely used for catalyst carriers, various filters, etc. Recently, the honeycomb structure has particularly attracted the attention as a diesel particulate filter (DPF) for capturing particulate matters discharged from a diesel engine.
Such honeycomb structure can generally be obtained by kneading a raw material composition obtained through addition of an auxiliary forming agent and various addition agents to a ceramic material and dispersion media such as water to form a kneaded clay, then extruding the kneaded clay into a honeycomb-shaped formed body (honeycomb formed body), drying this honeycomb formed body, and then firing the honeycomb formed body.
As means for drying honeycomb formed bodies, there have been known a natural drying method in which the honeycomb formed bodies are simply left under a room temperature condition, a hot-air drying method in which the honeycomb formed bodies are dried by a hot air generated with a gas burner etc., a dielectric drying method in which high-frequency energy is utilized, a microwave drying method in which microwaves are utilized, etc.
Among them, dielectric drying is performed by causing a current to flow between opposing electrode plates that are provided at an upper side of an opening top end surface and at a lower side of an opening bottom end surface of the honeycomb formed body, and by making water molecules in the honeycomb formed body in motion with high-frequency energy to generate frictional heat.
In the dielectric drying, densities of electric lines of force that pass through the honeycomb formed body easily become non-uniform, thereby partial drying delay occurs in the honeycomb formed body, and as a result of it, problems, such as variation in size and cracks, may occur in the obtained honeycomb structure. Consequently, there have been developed, for example, a method of employing a drying tray comprised of a perforated plate with high conductivity as shown in Patent Document 1, and further, for example, a method of placing a top plate with high conductivity on the opening top end surface of the honeycomb formed body as shown in Patent Document 2, and thereby it becomes possible to decrease partial diameter differences caused in the honeycomb structure and to reduce occurrence of the cracks by uniformizing the densities of the electric lines of force.
[Patent Document 1] JP-B-60-37382
[Patent Document 2] JP-A-63-166745